/*    
 * A* algorithm implementation.
 * Copyright (C) 2007, 2009 Giuseppe Scrivano <gscrivano@gnu.org>

 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
                       
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see <http://www.gnu.org/licenses/>.
 */
package pathfinder;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.PriorityQueue;

/**
 * A* algorithm implementation using the method design pattern.
 *
 * @author Giuseppe Scrivano
 */
public abstract class AStar<T>
{
                private class Path implements Comparable{
                                public T point;
                                public Double f;
                                public Double g;
                                public Path parent;
                               
                                /**
                                 * Default c'tor.
                                 */
                                public Path(){
                                                parent = null;
                                                point = null;
                                                g = f = 0.0;
                                }

                                /**
                                 * C'tor by copy another object.
                                 *
                                 * @param p The path object to clone.
                                 */
                                public Path(Path p){
                                                this();
                                                parent = p;
                                                g = p.g;
                                                f = p.f;
                                }

                                /**
                                 * Compare to another object using the total cost f.
                                 *
                                 * @param o The object to compare to.
                                 * @see       Comparable#compareTo()
                                 * @return <code>less than 0</code> This object is smaller
                                 * than <code>0</code>;
                                 *        <code>0</code> Object are the same.
                                 *        <code>bigger than 0</code> This object is bigger
                                 * than o.
                                 */
                                public int compareTo(Object o){
                                                Path p = (Path)o;
                                                return (int)(f - p.f);
                                }

                                /**
                                 * Get the last point on the path.
                                 *
                                 * @return The last point visited by the path.
                                 */
                                public T getPoint(){
                                                return point;
                                }

                                /**
                                 * Set the
                                 */
                                public void setPoint(T p){
                                                point = p;
                                }
                }

                /**
                 * Check if the current node is a goal for the problem.
                 *
                 * @param node The node to check.
                 * @return <code>true</code> if it is a goal, <code>false</else> otherwise.
                 */
                protected abstract boolean isGoal(T node);

                /**
                 * Cost for the operation to go to <code>to</code> from
                 * <code>from</from>.
                 *
                 * @param from The node we are leaving.
                 * @param to The node we are reaching.
                 * @return The cost of the operation.
                 */
                protected abstract Double g(T from, T to);

                /**
                 * Estimated cost to reach a goal node.
                 * An admissible heuristic never gives a cost bigger than the real
                 * one.
                 * <code>from</from>.
                 *
                 * @param from The node we are leaving.
                 * @param to The node we are reaching.
                 * @return The estimated cost to reach an object.
                 */
                protected abstract Double h(T from, T to);


                /**
                 * Generate the successors for a given node.
                 *
                 * @param node The node we want to expand.
                 * @return A list of possible next steps.
                 */
                protected abstract List<T> generateSuccessors(T node);


                private PriorityQueue<Path> paths;
                private HashMap<T, Double> mindists;
                private Double lastCost;
                private int expandedCounter;

                /**
                 * Check how many times a node was expanded.
                 *
                 * @return A counter of how many times a node was expanded.
                 */
                public int getExpandedCounter(){
                                return expandedCounter;
                }

                /**
                 * Default c'tor.
                 */
                public AStar(){
                                paths = new PriorityQueue<Path>();
                                mindists = new HashMap<T, Double>();
                                expandedCounter = 0;
                                lastCost = 0.0;
                }


                /**
                 * Total cost function to reach the node <code>to</code> from
                 * <code>from</code>.
                 *  
                 * The total cost is defined as: f(x) = g(x) + h(x).
                 * @param from The node we are leaving.
                 * @param to The node we are reaching.
                 * @return The total cost.
                 */
                protected Double f(Path p, T from, T to){
                                Double g =  g(from, to) + ((p.parent != null) ? p.parent.g : 0.0);
                                Double h = h(from, to);

                                p.g = g;
                                p.f = g + h;

                                return p.f;
                }

                /**
                 * Expand a path.
                 *
                 * @param path The path to expand.
                 */
                private void expand(Path path){
                                T p = path.getPoint();
                                Double min = mindists.get(path.getPoint());

                                /*
                                 * If a better path passing for this point already exists then
                                 * don't expand it.
                                 */
                                if(min == null || min.doubleValue() > path.f.doubleValue())
                                                mindists.put(path.getPoint(), path.f);
                                else
                                                return;

                                List<T> successors = generateSuccessors(p);

                                for(T t : successors){
                                                Path newPath = new Path(path);
                                                newPath.setPoint(t);
                                                f(newPath, path.getPoint(), t);
                                                paths.offer(newPath);
                                }

                                expandedCounter++;
                }

                /**
                 * Get the cost to reach the last node in the path.
                 *
                 * @return The cost for the found path.
                 */
                public Double getCost(){
                                return lastCost;
                }


                /**
                 * Find the shortest path to a goal starting from
                 * <code>start</code>.
                 *
                 * @param start The initial node.
                 * @return A list of nodes from the initial point to a goal,
                 * <code>null</code> if a path doesn't exist.
                 */
                public List<T> compute(T start){
                                try{
                                                Path root = new Path();
                                                root.setPoint(start);

                                                /* Needed if the initial point has a cost.  */
                                                f(root, start, start);

                                                expand(root);
                                                
                                                ArrayList<List<T>> retorno = new ArrayList<List<T>>();
                                                for(;;){
                                                                Path p = paths.poll();
                                                    
                                                                if(p == null){
                                                                                lastCost = Double.MAX_VALUE;
                                                                                if(retorno.size() ==0)
                                                                              	  return null;
                                                                                else{
                                                                                	List<T> menor = retorno.get(0);
                                                                                	int min=99999999;
                                                                                	for(int i=0; i<retorno.size(); i++){
                                                                                		if(retorno.get(i).size() < min){
                                                                                			min = retorno.get(i).size();
                                                                                			menor = retorno.get(i);
                                                                                		}
                                                                                	}
                                                                                	return menor;
                                                                                	
                                                                                }
                                                                }

                                                                T last = p.getPoint();

                                                                lastCost = p.g;

                                                                if(isGoal(last)){
                                                                                LinkedList<T> retPath = new LinkedList<T>();
                                                                                
                                                                                for(Path i = p; i != null; i = i.parent){
                                                                                                retPath.addFirst(i.getPoint());
                                                                                }
                                                                                
                                                                                if(p==null)
                                                                                
                                                                                retorno.add(retPath);
                                                                            
                                                                                //return retPath;
                                                                                
                                                                }
                                                                expand(p);
                                                }
                                }
                                catch(Exception e){
                                                e.printStackTrace();
                                }
                                return null;
                                               
                }
}
